In mobile communication networks, it is known to direct data traffic of a certain type, e.g. related to a specific service or application, to a corresponding bearer. In this respect, a bearer is considered to be an information transmission context or path of defined characteristics, e.g. capacity, delay and/or bit error rate. Typically, a bearer allows for providing a desired quality of service (QoS). In this connection it is known to distinguish between guaranteed bit rate (GBR) bearers, in which a certain bit rate for transmitting the data traffic is guaranteed, and non-GBR bearers, in which there is no guaranteed bit rate for transmitting the data traffic.
According to the 3GPP (3rd Generation Partnership Project) technical specification 23.401, a bearer may be a concatenation of multiple sub-bearers: a radio bearer established between a mobile terminal and an access node, e.g. a base station or the like, an S1 bearer established between the access node and a serving gateway, and an S5/S8 bearer established between the serving gateway and a packet data network (PDN) gateway.
An established bearer may be dropped or released in certain events. A typical example is when the mobile terminal goes out of radio coverage. In this case the access node will release the radio bearer between the mobile terminal and the access node, which in turn causes the S1 bearer between the access node and the serving gateway to be released.
If for a non-GSR bearer the radio bearer and/or the S1 bearer is released, a so-called “bearer preservation” mode is entered. That is to say, the corresponding S5/S8 bearer is kept established.
The above behavior may result in problems with respect to the service layer not being notified of a loss of resources, e.g. a loss of the radio bearer or a loss of the S1 bearer. Since the S5/S8 bearer with respect to the PDN gateway is kept established, the PDN gateway does not become aware of a part of the bearer being lost and cannot notify any other service layer nodes of this event.
For example, according to the 3GPP specification 23.203, IMS signalling traffic (IMS: Internet Protocol Multimedia Subsystem) is typically mapped to a dedicated non-GBR bearer with QCI 5 (QCI: QoS Class Identifier). If such a non-GSR bearer is established, and the mobile terminal goes out of radio coverage, which causes the radio bearer to be dropped, IMS signalling is no longer possible between the IMS client on the mobile terminal and the IMS network. However, since the PDN gateway is not aware of the radio bearer being dropped, the IMS network will not be notified that IMS signalling is no longer possible.
Another example is charging of VoIP services (VoIP: Voice over Internet Protocol). Such services are typically charged within the service layer and not within the access network. In other words, for these services charging is typically not accomplished by a node which is aware of the radio bearer or the S1 bearer being active or not. If VoIP data traffic is mapped onto a non-GBR bearer, it is no longer possible that the service layer is notified if the radio bearer or the S1 bearer is lost, e.g. due to the mobile terminal going out of radio coverage. This in turn would cause charging at the service layer to continue, which is undesirable.
Accordingly, there is a need for efficient techniques for controlling the releasing of non-GBR bearers.